KR20220003372A - Photocatalytic Filters Having Physical Entrapment of Pollutants and Method for Purifying Gaseous Medium Using the Same - Google Patents

Abstract

According to the present disclosure, disclosed are an alveoli-simulating photocatalytic filter having a physical trapping structure in the form of an air pocket that is effective against contaminants in gaseous media such as the air, indoor air and the like, and a method for removing contaminants from gaseous media using the same.

Description

Photocatalytic Filters Having Physical Entrapment of Pollutants and Method for Purifying Gaseous Medium Using the Same

The present disclosure relates to a photocatalytic filter having a physical trapping structure of contaminants and a method for purifying a gaseous medium using the same. More specifically, the present disclosure relates to an alveoli-simulating photocatalytic filter having a physical trapping structure in the form of an air pocket that is effective against contaminants in a gaseous medium such as air, indoor air, etc. without using an adsorbent, and the same It relates to a method for removing contaminants in a gaseous medium using

Effective control of environmental pollution is emerging as a serious problem in urbanized and industrialized societies due to the rise of environmental rights that require a pleasant environment in human life and the reinforcement of policies or institutional regulations to support it. The formation of large-scale industrial areas and the formation of large cities due to urbanization and industrialization are caused by various air pollutants, such as nitrogen oxides (NOx), sulfur oxides (SOx), hydrocarbons (eg monocyclic or polycyclic aromatic hydrocarbons); It is causing an increase in air pollutants such as volatile organic compounds (VOCs).

VOC, which is a causative material of air pollution and generated in various industrial and service facilities, is known to have strong mobility in the air, cause odor, and have strong anesthesia, and act as a toxic substance to the nervous system. In addition, contaminants such as aromatic hydrocarbons including benzene and toluene have carcinogenicity. In addition, VOC acts as a factor that accelerates global warming by depleting the ozone layer in the stratosphere.

As such, VOC is not only harmful by itself, but also creates a photochemical oxidizer through a photochemical reaction in the atmosphere and acts as a precursor to cause secondary pollution, so harmful secondary air pollutants such as ozone, aldehyde, PAN (p-oxyacethlnitrate), etc. VOCs control is positioned as an important research field in air environment conservation, and countries around the world are adding strengthened policy measures to reduce VOC emissions. For example, the U.S. Environmental Protection Agency (EPA) has designated 189 compounds as hazardous air pollutants, of which 97 are of the VOC family. Even when these air pollutants are present in low concentrations, they act as dissatisfaction factors for the indoor environment for people who spend most of their time indoors, and have a direct adverse effect on health. In addition, civil complaints in adjacent areas are also on the rise due to odorous gases generated from VOC, various industries, sewage, livestock wastewater, and manure treatment plants. Therefore, various studies for removing air pollutants are being actively conducted.

Currently, various methods such as thermal incineration, adsorption, catalytic combustion, biofilter, adsorption, and oxidation using a photocatalyst have been developed as a control technology for air pollutants such as VOC.

Among the above-described methods, a method of _{oxidizing and removing VOCs using a photocatalyst such as UV/TiO 2} is attracting attention due to its eco-friendly characteristics and the like. Factors to be considered in the photocatalyst design are (i) that electron-hole pairs can be formed and their recombination must be inhibited, and (ii) that VOC molecules must have physical access to the catalyst surface. can

For requirement (i), it relates to the formation of reactive oxygen species (ROS) that oxidize organic molecules and is determined by bandgap energy, band edge position, light absorption, and facet structure. However, a single unmodified catalyst (TiO ₂ , ZnO, MnO ₂ , Fe ₂ O ₃ , CuO, etc.) is difficult to meet these requirements, and does not work effectively, especially in gas phase photocatalytic reactions. Accordingly, a method of coupling two or more semiconductors (eg, Bi ₂ O ₃ and TiO ₂ ) has been proposed, and catalytic activity can be increased in the form of a complex due to the formation of a pn junction. However, due to insufficient ROS generation and recombination of charge carriers, it can still cause loss of photoconversion reaction.

For requirement (ii), after optimized adsorption, the migration of gaseous compounds to the active site of the catalyst is an essential element for initiating the photochemical reaction. However, the aforementioned inorganic metal oxide is applied in the form of a catalyst layer, but is not preferred due to its low adsorption capacity. For this reason, attempts have been made to promote mass transfer by incorporating strong organic adsorbents into the catalyst structure. In this regard, although the organic adsorbent support is effective in facilitating the transfer of gaseous contaminants from air to the catalyst bed, both the VOC and the adsorbent are organic and thus remain on the support, which is inefficient in transferring contaminants to the catalyst surface. In addition, the hybrid catalyst/adsorbent composite can improve mass transfer between the adsorbent and the catalyst by maximizing interfacial contact, and can exhibit good catalyst performance, especially at low VOC concentrations. However, at a high concentration, the catalyst active site may be blocked due to mass movement of excessive VOCs. Accordingly, there is a need for a method capable of exhibiting good photocatalytic performance at both low and high concentrations, particularly problems of the prior art.

An embodiment of the present disclosure solves the problems of the conventional photocatalyst for removing air pollutants, and in particular, provides a catalyst capable of effectively photooxidizing and removing air pollutants under high concentration conditions as well as low concentration conditions.

In another embodiment of the present disclosure, an object of the present disclosure is to provide a method capable of effectively removing and purifying pollutants in the atmosphere (indoor), particularly organic pollutants such as VOCs, using the above-described catalyst.

According to the first aspect of the present disclosure,

substrates in the form of strands;

a nanorod array radially formed on the surface of the strand-shaped substrate in the longitudinal direction; and

a porous first photocatalyst layer formed on the nanorod array;

includes,

Here, as the porous first photocatalyst layer is coated on the nanorod array, there is provided a photocatalytic filter that forms a physical trapping structure in the form of an air pocket.

According to an exemplary embodiment, the porous first photocatalyst layer is made of NiMoO ₄ , NiCo ₂ O ₄ , NiCo ₂ S ₄ , CdS, Bi ₂ WO ₆ , SnO ₂ , ZrO ₂ , Fe ₂ O ₃ , and WSe ₂ . It may be a material selected from the group consisting of at least one.

According to an exemplary embodiment, the photocatalytic filter further includes a second photocatalyst layer in the form of a thin film sheet coated on the porous first photocatalyst layer, wherein the second photocatalyst layer is carbon nitride (C ₃ N ₄ ) , silicon carbide (SiC), gallium nitride (GaN), graphene oxide, carbon quantum dots, silver chloride (AgCl), silver bromide (AgBr), zinc selenide (ZnSe), cerium oxide (CeO) ₂ ), and may include at least one selected from the group consisting of cadmium sulfide (CdS).

According to a second aspect of the present disclosure,

a) providing a substrate in the form of strands;

b) contacting the precursor solution for forming nanorods with the substrate in the form of strands to radially form a nanorod array along the length direction thereof; and

c) contacting the photocatalyst precursor solution with the nanorod array to form a porous first photocatalyst layer on the nanorod array;

includes,

Herein, there is provided a method of manufacturing a photocatalytic filter in which a porous first photocatalyst layer is coated on the nanorod array to form a physical trapping structure in the form of an air pocket.

According to an exemplary embodiment, the step b),

b1) forming a seed layer of the nanorods on the strand-shaped substrate; and

b2) performing a hydrothermal synthesis reaction by contacting the precursor solution for forming the nanorods to the substrate on which the seed layer is formed;

may include

According to a third aspect of the present disclosure,

A method for removing contaminants in a gaseous medium comprising:

providing a photocatalytic filter; and

oxidizing and removing the contaminants in the gaseous medium by contacting the contaminant-containing gas with the photocatalytic filter under ultraviolet irradiation,

Here, the photocatalytic filter,

substrates in the form of strands;

a nanorod array radially formed on the surface of the strand-shaped substrate in the longitudinal direction; and

a porous first photocatalyst layer formed on the nanorod array;

includes,

Here, there is provided a method of forming a physical trapping structure in the form of an air pocket as the porous first photocatalyst layer is coated on the nanorod array.

According to an embodiment of the present disclosure, conventionally, a photocatalytic reaction is performed by transferring contaminants (especially organic contaminants such as VOCs contained in gaseous media such as atmospheric and indoor air) to the catalyst surface using an adsorbent. In order to overcome the limitation in removing high concentrations of contaminants in By emitting to the photocatalyst surface, excellent decomposition efficiency can be exhibited for not only low concentration pollutants but also high concentration pollutants.

Furthermore, the above-described photocatalytic filter can be applied immediately in the field by replacing or adding only a photocatalyst without requiring special changes to the existing facility that applies ultraviolet rays, and also has good resolution even when repeatedly used (or reused) can provide Therefore, widespread commercialization is expected in the future.

1 shows a schematic structure and an SEM photograph of a photocatalytic filter having a physical trapping structure in the form of an air pocket according to an exemplary embodiment;
2 is a view showing a method of manufacturing a photocatalytic filter according to an embodiment step by step;
3 is, (a, b) SEM pictures of bare stainless steel mesh (SSM), (c, d, e) SEM pictures of ZnO nanorods grown on SSM, (f) TEM pictures of ZnO nanorods , (g, h) SEM pictures of _{ZnO/NiMoO 4 catalyst on SSM (NiMoO 4} grown by two adhesion cycles), (i) C _{3 modified with 0.1 M NaOH and attached on ZN@SSM} SEM picture of N ₄ , (jo) EDS mapping of ZNC@SSM for elemental analysis and spatial distribution analysis;
4 shows (a, b) SEM photos of ZnO nanorods formed on SSM in the absence of a seed layer, (c) _{TEM photos of NiMoO 4} nanoplates, (d, e) growth by single and two attachment cycles. SEM pictures of each NiMoO ₄ layer, (f, g) SEM pictures of intrinsic and modified C ₃ N ₄ (0.2 M NaOH) _{attached to ZN@SSM, (h) mC 3} N ₄ (0.1 M NaOH) is a TEM picture of a thin sheet;
Figure 5 is (a) XRD spectrum of the catalyst, (b, c) a view showing vertical and random growth of ZnO nanorods formed respectively in the presence or absence of a seed layer, (d, e) two types, formed on SSM; ZnO nanorod tips of (f, g) are diagrams showing the different morphological characteristics of _{NiMoO 4 catalysts grown on SSM and Z@SSM;}
Figure 6 is (ae) XPS spectrum of the catalyst to determine the elemental oxidation state, (f) UV-vis absorption spectrum of the catalyst, (g) Tauq plot for determining the bandgap of the catalyst, (h) the band of the catalyst gap and band edge locations;
7 is a diagram showing (a, b) a toluene adsorption pattern and mechanism of the catalyst, (c, d) a toluene desorption pattern and mechanism of the catalyst;
8 is a photograph showing a photocatalytic glass reactor used for a toluene decomposition reaction;
9 is, (a) a graph showing the photocatalytic toluene decomposition test results shown by the catalyst, (b) _{a graph showing the effect of the C 3} N ₄ type on the toluene decomposition reaction, (c) C ₃ N ₄ petals before attachment ( petals) _{SEM photograph of NiMoO 4} , (d, e, f) SEM photograph of petal-shaped NiMoO _{4 with C 3} N ₄ attached with native, 0.1 M NaOH and 0.2 M NaOH treatment, (g, h, I) TEM images of native, 0.1 M NaOH and 0.2 M NaOH treated C ₃ N _{4 , respectively;}
10 is a graph showing toluene removal rates by photolysis and adsorption at different inlet gas concentrations;
_{11 is a SEM photograph of NiMoO 4} prepared by (a, b, c) 1, 2 and 3 adhesion cycles, respectively, (d, e, f) NiMoO ₄ adhesion cycle on molecular diffusion in the air pocket It is a drawing showing the impact;
12 is, (a) a graph showing the effect of temperature control on toluene decomposition by ZNC@SSM, (b) a graph showing the effect of relative humidity (%) on toluene decomposition by ZNC@SSM, (c) A graph showing the toluene decomposition inhibitory effect on the scavenger, (d) a diagram showing the catalyst active point and potential for toluene decomposition;
13 is a graph showing the effect of reuse and washing of an air filter on toluene decomposition;
14 shows (a) SEM pictures of ZNC@SSM before and after 10 disintegration cycles, (b) XRD spectrum showing crystal integrity of the composite after reuse test, (cf) XPS of ZNC@SSM before and after 10 disintegration cycles. is the spectrum; and
15 is a diagram showing a toluene decomposition path under conditions of low relative humidity and high relative humidity.

The present invention can all be achieved by the following description. It is to be understood that the following description describes preferred embodiments of the present invention, and the present invention is not necessarily limited thereto. In addition, the accompanying drawings are provided to aid understanding, and the present invention is not limited thereto, and details regarding individual configurations may be properly understood by the specific purpose of the related description to be described later.

A “volatile organic compound (VOC)” can be defined as an organic compound having a boiling point of about 50 to 260°C, typically under ambient temperature and pressure conditions.

"Photocatalyst" may mean a heterogeneous catalyst, specifically a solid-phase catalyst, that promotes a reaction in the presence of light but is not consumed in the overall reaction. Typically, a photocatalyst is (i) photoactive, (ii) utilizing near-UV light, (iii) biologically and chemically inert, (iv) photo-stable, and (v) may have properties that indicate non-toxicity.

“Substrate” may mean a structure or structure that provides a surface capable of being attached (fixed) or coated (applied) thereon, and may have a one-dimensional, two-dimensional, or three-dimensional shape.

A “nanostructure” or “nanostructure” refers to a feature or texture having a dimension or size on the nanoscale (e.g., about 0.1 to 1,000 nm, specifically 1 to 100 nm), e.g. For example, it may mean an arbitrary nanoscale object including nanopillars, nanorods, nanowalls, nanowires, nanowebs, and the like.

“Nanorods” may refer to rods having a diameter of about 1,000 nm or less, for example, in the range of several nanometers to several hundreds of nanometers.

"Array" means fibers, columns, rods, pillars, loops, tubes, cones, blocks, cubes, hemispheres derived from or attached to (fixed) to a support, member or backing member. , can be broadly construed to mean a morphological feature, texture, or surface, including a spare, wall, grid, hole, or combination thereof.

Although "contacting" in a narrow sense means direct contact between two objects, it may be understood that any additional element may be interposed in a broad sense.

It may be understood that the expressions “on” and “on” are used to refer to the concept of relative position. Accordingly, in addition to the case where other components or layers are directly present in the aforementioned layer, other layers (intermediate layers) or components may be interposed or present therebetween, and are formed by partially overlapping the space between the members. It may also be included in the form of Similarly, the expressions “under”, “under” and “below” and “between” may also be understood as relative concepts with respect to location. Also, the expression “sequentially” may be understood as a concept of relative position.

In the present specification, when a component is "included", it means that other components and/or steps may be further included, unless otherwise specified.

A. Photocatalytic filter with physical trapping structure

1 is a schematic structure and SEM photograph of a photocatalytic filter having a physical trapping structure in the form of an air pocket according to an exemplary embodiment.

The most important step in the photocatalytic oxidation reaction is the formation of a hole-electron pair that requires energy to overcome a band gap between a valence band and a conduction band. When the light energy equals or exceeds the band gap energy, a hole-electron pair is formed in the catalyst, which is decomposed into photoelectrons in the conduction band and photoholes in the valence band, respectively. At the same time, photo oxidation and reduction reactions occur in the presence of air, oxygen, and contaminants, and the oxidation of moisture in the air adsorbed during the reaction process or the reactivity of hydroxy radicals derived from ^{OH − are high.} In addition, due to the reducing ability of electrons, molecular oxygen is induced to be reduced to a ^{superoxide radical (O 2 - ).} These highly reactive species, hydroxyl groups and superoxide radicals, can provide strong resolution for contaminants (specifically organic contaminants such as VOCs) in gaseous media.

Referring back to FIG. 1 , a plurality of nanorods (ie, nanorod arrays) are radially disposed on a surface (specifically, a circumferential surface) of a strand-shaped substrate in the longitudinal direction thereof.

According to the illustrated embodiment, since the porous photocatalyst layer is disposed on the nanorod array, the porous photocatalyst layer may be formed in a shape similar to flower petals on the nanorod array. In this way, the physical trapping structure in the form of air pockets can be formed only when the porous photocatalyst layer is coated (or covered) on the nanorod array, and as a result, as it comes into contact with a gaseous medium such as the atmosphere, in the gaseous medium Contaminants may be physically trapped (or trapped) within the air pockets.

In this regard, the aforementioned physical trapping structure has a structure similar to human alveoli or alveoli, which may mean a small balloon-shaped structure in the respiratory system of the human body, and its total surface area is about 70 m , which is significantly larger than the relative volume of the lungs. The retention of air in the alveoli and its large surface area act collectively to enable the lungs to perform respiratory functions within the body.

Meanwhile, according to an exemplary embodiment, the strand-type substrate is not particularly limited as long as it has characteristics that exhibit stability upon exposure to light, contaminants and by-products such as VOCs, and photocatalysis. In this case, the cross-section of the substrate may be, for example, a circle, a triangle, a quadrilateral (eg, a square or a rectangle), a pentagon, a hexagon, an octagon, an oval, and the like, and more specifically, a circular cross-section. can have In addition, the material of the substrate may be selected from any metal or metal alloy substrate such as stainless steel (SUS), nickel foam, copper foam, glass, aluminum foil, and the like, but this may be understood as illustrative. However, it may be advantageous to use a stainless steel material in terms of stability and economy.

According to an exemplary embodiment, the cross-sectional diameter of the substrate in the form of a strand may be determined within the range of, for example, about 30 to 100 μm, specifically about 40 to 70 μm, and more specifically about 45 to 55 μm, It is not necessarily limited to this.

According to a specific embodiment, the substrate may use a substrate in the form of a single strand, or alternatively, a substrate in the form of a plurality of strands may be used in the form of a combined structure, for example, a mesh structure, a porous metal/non-metal It can be applied to foam, woven/non-woven fabric, and the like.

However, in the case of a mesh structure, since the pore size of the mesh may be considered, it is preferable not to reduce the surface area required for growth of nanorods (and photocatalytic components) to be described later while allowing air to permeate therethrough. In this regard, the pore size of the mesh may be, for example, in the range of about 50 to 150 μm, specifically about 70 to 120 μm, and more specifically about 80 to 100 μm, but this may be understood as an example.

On the other hand, the nanorod array formed on the strand-type substrate provides a function of supporting the air pocket-type physical trapping structure.

According to an exemplary embodiment, the size (diameter) of the individual nanorods constituting the nanorod array is, for example, in the range of about 50 to 150 nm, specifically about 70 to 130 nm, more specifically about 90 to 110 nm. can Further, the length of individual nanorods in the nanorod array may be, for example, in the range of about 400 to 600 nm, specifically about 450 to 550 nm, and more specifically about 480 to 520 nm. In addition, the aspect ratio of the individual nanorods may be, for example, in the range of about 4 to 12, specifically about 6 to 11, and more specifically about 8 to 10.

In addition, the material of the nanorod array can be selected from, for example, a transition metal, specifically, a transition metal oxide. As an example, zinc oxide (ZnO), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), cobalt oxide (Co ₃ O ₄ ), tin oxide (SnO ₂ ), nickel oxide (NiO), manganese oxide (MnO) ₂ ) and the like, and specifically zinc oxide. In particular, when zinc oxide is used, it is advantageous because it can exhibit excellent stability and electron mobility, and has selective adsorption properties for organic molecules such as VOCs.

In an exemplary embodiment, the porous first catalyst layer may be formed on the nanorod array in the shape of a flower petal-shaped thin film plate, specifically, a hexagonal thin film plate shape. In this regard, the size (average size) of the thin film plate may be, for example, selected within a range of about 200 to 400 nm, specifically about 250 to 350 nm, and more specifically about 290 to 310 nm.

According to one embodiment, the physical trapping structure in the form of an air pocket may not only provide a large specific surface area, but also provide a trapping function for contaminants in a gaseous medium, particularly VOCs, in the photocatalytic filter structure. In this case, the porous first photocatalyst layer may have a property through which the gaseous medium can be exchanged. As a result, there is no need to capture contaminants from the atmosphere using strong adsorbents as in the prior art, and a concentration gradient-based diffusion process can be used to avoid the limitations of adsorbent-catalyst systems.

Specifically, in the porous first photocatalyst layer, a concentration gradient occurs because the concentration of contaminants in the outer gaseous medium (atmosphere, indoor air, etc.) is higher than in the air pockets, and this concentration gradient moves molecules of the contaminants into the air pockets. It provides a driving force that can transmit or move. As such, molecular diffusion may occur from the air into the catalyst having a structure similar to that of the alveoli through the selective adsorption and concentration gradient of nanorods (particularly, ZnO nanorods) with respect to organic pollutant molecules.

On the other hand, the trapped contaminants may remain trapped within the air pocket, and may be released slowly or in a controllable manner and decomposed by the first photocatalyst layer (or the first photocatalyst layer and the second photocatalyst layer to be described later) ( It has a suitable band edge position to facilitate charge separation and reactive oxygen species (ROS) generation). In this regard, when the first photocatalyst layer is insufficiently formed, the trapped contaminant molecules can be easily discharged across the pores of the photocatalyst layer even if they enter the air pockets. On the other hand, when the first photocatalyst layer has an excessively small pore size or excessive thickness (ie, a path for contaminant particles to move from the outside into the air pocket is limited by forming an excessively dense or dense state), the concentration gradient In spite of the generation of driving force by

Therefore, the first photocatalyst layer provides a property that contaminant molecules can cross the catalyst layer and enter into the air pocket by molecular diffusion according to the concentration gradient, and the trapped contaminant molecules are not easily discharged from the air pocket. it can be advantageous To this end, at least one may be adjusted from the pore size and thickness of the first photocatalyst layer, the number of catalyst layers (or the number of layers), and the like.

In addition, the first photocatalyst layer may consist of one layer or two or more layers, and correspondingly, it is possible to determine the number of deposition or coating steps of the photocatalyst layer. As an example, the total thickness of the first photocatalyst layer may be, for example, in the range of about 200 to 800 nm, specifically about 300 to 700 nm, more specifically about 400 to 600 nm, and may consist of two or more layers. In this case, the thickness of the individual catalyst layers may range, for example, from about 100 to 300 nm, specifically from about 200 to 280 nm, and more specifically from about 220 to 260 nm.

According to an exemplary embodiment, the porous first photocatalyst layer may be grown on a nanorod array and may be selected from a modification having properties capable of forming a plate structure of an appropriate size (if the plate size is too small, This is because the physical trapping structure in the form of air pockets can be blocked by passing through the nanorods). The band gap of this first photocatalyst layer may range, for example, from about 2.3 to 3.5 eV, specifically from about 2.4 to 3.2 eV, and more specifically from about 2.5 to 2.8 eV. In this regard, the material of the first photocatalyst layer is, for example, metal molybdate (MMoO ₄ ) (M is selected from group VIII and group IB metals, specifically Ni, Co, Fe or Cu), NiCo ₂ O ₄ , NiCo ₂ S ₄ , CdS, Bi ₂ WO ₆ , SnO ₂ , ZrO ₂ , Fe ₂ O ₃ , and WSe ₂ may be at least one selected from the group consisting of. More specifically, the first photocatalyst layer may be made of a nickel molybdate (NiMoO ₄ ) material, and NiMoO ₄ has a narrow band gap of about 2.54 eV, and is low-cost and environmentally friendly. Moreover, it has favorable stability also with respect to ultraviolet irradiation, a by-product of a photocatalytic reaction, etc. In particular, it may be advantageous in that it can be attached only to the nanorod array, and a plate structure of an appropriate size can be formed.

Meanwhile, according to an exemplary embodiment, the photocatalytic filter may be combined with the above-described first photocatalyst layer to form a composite, and may further include a second photocatalyst layer. Illustratively, the second photocatalyst layer may form a heterojunction structure with respect to the first photocatalyst layer, and its band edge position may be less than about -0.1 eV to form superoxide radicals. In addition, the second photocatalyst layer can be selected from a type that does not block or block pores in the first photocatalyst layer while being able to coat the first photocatalyst layer in the form of a thin film.

As an example, the second photocatalyst layer in the photocatalytic filter may be included to cover or surround the first photocatalyst layer in the form of a thin film sheet. According to an exemplary embodiment, the second photocatalyst layer may exhibit a porous amorphous structure.

At this time, the material of the second photocatalyst layer is carbon nitride (C ₃ N ₄ ), silicon carbide (SiC), gallium nitride (GaN), graphene oxide, carbon quantum dots, silver chloride (AgCl) ), silver bromide (AgBr), zinc selenide (ZnSe), cerium oxide (CeO ₂ ), and cadmium sulfide (CdS) may be at least one selected from the group consisting of, specifically carbon nitride (C ₃ N ₄ ), More specifically, alkali-modified carbon nitride (mC ₃ N ₄ ) may be used. As such, by further including the alkali-modified second photocatalyst layer, the porous photocatalyst layer formed on the nanorod array may exhibit more uniform porosity. In this case, at least one selected from sodium hydroxide, KOH, and the like may be used for alkali modification. However, when it is modified with an excessively large amount of alkali, it may be advantageous to use the alkali-modified second photocatalyst layer to an appropriate level as much as it can block or clog the pores of the underlying first photocatalyst layer. In addition, it may be advantageous that the second photocatalyst layer has a thickness that is insignificant compared to the thickness of the first photocatalyst layer. However, the pore size of the photocatalyst layer may be changed by forming the second photocatalyst layer.

In addition, the band gap can also be slightly changed by covering with the second photocatalyst layer, for example, when the first photocatalyst layer is formed, when the band gap is about 2.6 eV, the second photocatalyst layer is formed thereon In this case, it may be at a level of about 2.44 eV.

As such, the catalyst having a structure similar to that of the alveoli has properties suitable for decomposition of contaminants in a gaseous medium such as indoor and outdoor air, specifically VOCs, particularly aromatic components such as toluene.

Manufacturing method of photocatalytic filter

According to another embodiment of the present disclosure, there is provided a method of manufacturing a photocatalytic filter provided with a physical trapping structure in the form of an air pocket.

First, a substrate in the form of a strand is provided, and details thereof are as described above. Then, the step of forming the nanorod array on the substrate is performed.

In this regard, the nanorods are, as described above, a transition metal, specifically, a transition metal oxide material, and a method known in the art, for example, a vapor-liquid-solid process (VLS), electroplating method, sol-gel method, MOCVD The bar may be formed on the substrate through (metal-organic chemical vapor deposition), hydrothermal synthesis, solvothermal synthesis, or the like. Typically, hydrothermal synthesis (or solvothermal synthesis) may be used.

Hereinafter, a method of forming a nanorod array through hydrothermal synthesis will be mainly described. Specifically, a wet growth method using a transition metal oxide precursor solution, specifically a transition metal ion-containing precursor solution may be used. In this case, as the solvent used in the transition metal ion-containing precursor solution, for example, a C1-4 alcohol and/or water, specifically ethanol, isopropanol, and/or water, more specifically water, may be exemplified.

According to an exemplary embodiment, the transition metal usable for forming the nanorods in this embodiment is, for example, zinc (Zn), zirconium (Zr), titanium (Ti), cobalt (Co), tin (Sn), At least one may be selected from the group consisting of nickel (Ni) and manganese (Mn), and more specifically, zinc (Zn). In addition, the transition metal may be nitrate, sulfate, acetate, formate, halide, hydroxide, a combination thereof, or a hydrate thereof.

According to a specific embodiment, the transition metal may be zinc, and the zinc precursor may be a water-soluble zinc compound (or salt), specifically zinc nitrate, zinc sulfate, zinc acetate, zinc formate, zinc (II) chloride, zinc iodide. Zinc, a hydrate thereof, etc. may be used, and these may be used alone or in combination. More specifically, zinc acetate can be used because zinc acetate has good affinity for a strand-type substrate, particularly a substrate made of stainless steel.

In this regard, the concentration of the transition metal precursor (transition metal ion) in the precursor solution is a factor that can affect the density of the nanorods, for example, nucleation generated on the substrate as the concentration of the transition metal ion increases. points will increase. In consideration of this, the concentration of the transition metal precursor in the precursor solution is, for example, about 1 to 100 mM, specifically about 10 to 60 mM, more specifically about 20 to 40 mM, particularly about 25 to 30 mM. can be a range. When the concentration of the transition metal precursor is excessively low or high, it may be advantageous to control the transition metal oxide within the above-mentioned range as much as it is difficult to generate the transition metal oxide. However, the concentration range is exemplary and may be changed in consideration of reaction conditions, the shape and size of a desired nanorod array, and the like.

For the hydrothermal synthesis reaction, the transition metal precursor-containing aqueous solution further contains at least one additive component (including a reducing agent) that enables the precursor to be converted into an oxide and grow in a specific plane direction (eg, one-dimensional direction) on the substrate at the same time. may include Examples of such an additive component may be hexamethylenetetraamine, ethylenediamine, ammonia, polyethyleneimine, urea, or a combination thereof. In particular, the above-described additive component affects the morphological characteristics of the nanorods during the hydrothermal synthesis reaction, and specifically serves to promote or inhibit the growth of a specific crystal plane. That is, the precursor is converted into an oxide and grows in a one-dimensional structure like a nanorod, thereby inhibiting lateral growth.

In this regard, the nanorod array may grow anisotropically with respect to the surface of the substrate, specifically in a perpendicular or non-perpendicular direction, but with respect to the surface of the substrate, for example, about 60 to 120° , specifically about 70 to 110°, more specifically about 80 to 100°, particularly, in a substantially vertical direction (specifically, crystal growth).

Illustratively, the total concentration of the addition component in the transition metal ion-containing solution may be appropriately adjusted within the range of about 5 to 80 mM, specifically about 10 to 70 mM, and more specifically about 20 to 60 mM.

Further, according to an exemplary embodiment, the molar ratio of the transition metal:addition component in the precursor-containing solution is, for example, from about 0.3 to 3:1, specifically from about 0.4 to 2:1, more specifically from about 0.5 to It may be a range of 1:1, but this may be understood as an example.

According to a specific embodiment, the additive component may contain a combination of hexamethylenetetraamine and urea, wherein hexamethylenetetraamine functions as a reducing agent, while urea induces the formation of an array of one-dimensional structures. In this case, the molar ratio of hexamethylenetetraamine/urea may be, for example, about 0.3 to 5, specifically about 0.5 to 2, and more specifically about 0.6 to 1.5.

In an exemplary reaction system, when the transition metal is zinc, the zinc precursor in the precursor solution is according to the following Scheme 1 (when ammonia is used as the reducing agent) or Scheme 2 (when using hexamethylenetetraamine as the reducing agent) As it is converted to zinc oxide, it grows in a one-dimensional shape such as a nanorod on a strand-type substrate.

[Scheme 1]

[Scheme 2]

Meanwhile, the reaction time and temperature during hydrothermal synthesis affect the form of the transition metal oxide, and the reaction temperature is, for example, about 60 to 150° C., specifically about 70 to 130° C., and more specifically about 90 to 120° C. range, and the reaction (heat treatment) time may range, for example, from about 1 to 48 hours, specifically from about 3 to 20 hours, and more specifically from about 5 to 10 hours. At this time, the diameter of the nanorods can typically change with the reaction time, for example, grow at a rate of about 0.5 to 10 μm/hr, specifically about 1 to 2 μm/hr, depending on the reaction (heat treatment) time. However, this may be understood in an exemplary sense.

As described above, by crystal growth from a plurality of nucleation points, a nanorod array made of a transition metal oxide material may be radially formed along the length direction of the strand-shaped substrate.

Meanwhile, as described above, the step of forming a seed layer on the surface of the strand-shaped substrate prior to the reaction may be selectively performed so that the nanorods can be easily grown by the hydrothermal synthesis method. Such a seed layer may act as a nucleation spot on which a transition metal oxide (eg, zinc oxide) can grow. For example, it may be a crystallized seed layer or a single crystal transition metal oxide layer. According to an exemplary embodiment, as a method for forming the seed layer, it may be formed by a method of contacting a seed solution of a transition metal oxide with a substrate, a physical method (vapor deposition, sputtering, etc.).

As an example, when using a seed solution, for example, a precursor solution (concentration: for example about 5 to 30 mM, specifically about 8 to 20 mM, more specifically about 10 to 15 mM) is applied onto a substrate, for example. For example, it is possible to form a seed layer by contacting it by dipping, impregnation, etc., and heat treatment (eg, about 200 to 500° C., specifically about 300 to 400° C.) in an oxygen-containing atmosphere. Washing (specifically alcohol (ethanol) washing) and/or drying may be performed. In addition, ultrasonic treatment may optionally be accompanied in order to form a solid seed layer during the coating process or after coating.

Meanwhile, as described above, after the substrate on which the nanorod array is formed, that is, the nanorod/substrate structure is formed, the step of forming the porous first photocatalyst layer may be performed.

In this regard, the porous first photocatalyst layer may be, for example, a metal molybdate (MMoO ₄ ) (M is selected from group VIII and group IB metals, specifically Ni, Co, Fe or Cu), NiCo ₂ O ₄ , NiCo ₂ S ₄ , CdS, Bi ₂ WO ₆ , SnO ₂ , ZrO ₂ , Fe ₂ O _{3 , and WSe 2} may be at least one selected from the group consisting of, and below, the first metal molybdate-based first The preparation of the photocatalyst layer will be mainly described.

According to an exemplary embodiment, the precursor (source) of the metal (M) is not particularly limited as long as it is soluble in water or acid, but for example, inorganic compounds such as oxides, hydroxides, nitrates, sulfates, carbonates; organic acid salts such as acetate and oxalate; It may be at least one selected from organometallic complexes such as acetylacetonate complexes and metal alkoxides.

Illustratively, when the metal (M) is nickel, nickel hydroxide, nickel nitrate, nickel sulfate, nickel carbonate, nickel acetate, nickel oxalate, nickel citrate, nickel benzoate, nickel 2-ethylhexylate, bis(acetylacetonate) Nickel etc. are mentioned. When metal (M) is cobalt, cobalt nitrate, cobalt (III) acetylacetonate, cobalt acetate, cobalt oxalate, etc. can be illustrated. When the metal (M) is iron, Fe such as iron(II) nitrate, iron(II) sulfate, iron(II) acetate, and iron(II) halide (eg, FeCl ₂ , FeBr ₂ , and FeI ₂ ) (II) compounds, and Fe(III) such as iron(III) nitrate, iron(III) sulfate, iron(III) acetate, and iron(III) halide (eg, FeCl ₃ , FeBr ₃ , and FeI ₃ ). ) may be used at least one selected from compounds. In addition, when the metal (M) is copper, at least one selected from copper nitrate, copper sulfate, copper acetate, copper formate, copper (II) chloride, and copper iodide may be used.

The molybdenum precursor (source) is, for example, molybdenum oxide, ammonium molybdate, sodium molybdate, potassium molybdate, rubidium molybdate, cesium molybdate, lithium molybdate, molybdenum 2-ethylhexylate, bis(acetylaceto nate) may be at least one selected from oxo molybdenum and the like.

According to an exemplary embodiment, a precursor solution containing the aforementioned metal (M) precursor and the molybdenum precursor may be prepared. In this case, as the solvent, C1-4 alcohol and/or water, specifically ethanol, isopropanol, and/or water, more specifically water, may be used. In addition, the pH of the precursor solution can be maintained as neutral as possible, for this purpose, a base component, for example, at least one selected from hydroxide, urea, ammonia, ammonium carbonate, quaternary ammonium salt, and the like may be added.

According to an exemplary embodiment, the concentration of molybdenum in the precursor solution may range, for example, from about 1 to 50 mM, specifically from about 3 to 40 mM, more specifically from about 8 to 20 mM. In addition, the molar ratio of metal (M)/Mo in the precursor solution may be, for example, in the range of about 0.1 to 10, specifically about 0.3 to 7, and more specifically 0.8 to 2. The above numerical ranges are described for illustrative purposes, and the present disclosure is not necessarily limited thereto.

Next, the first photocatalyst layer may be formed by contacting the previously prepared nanorods/substrate structure with the photocatalyst precursor solution in a manner known in the art (eg, dipping, etc.). At this time, the contact with the nanorod / substrate structure is under elevated temperature conditions, for example, about 70 to 140 ° C. (specifically about 75 to 110 ° C., more specifically about 80 to 95 ° C.), for example, about It may be carried out for 4 to 12 hours (specifically about 5 to 10 hours, more specifically about 5 to 8 hours). Thereafter, optionally washing (specifically, washing with deionized water and/or drying may be performed. In addition, ultrasonic treatment may optionally be accompanied to remove residual precursors.

The process of attaching the first photocatalyst layer described above can be repeated two or more times for the purpose of increasing the thickness of the photocatalyst layer and controlling the inflow and outflow of contaminants in the appropriate gas phase. As a result, a first photocatalyst layer-nanorod/substrate structure can be obtained.

Meanwhile, according to one embodiment, a second photocatalyst layer in the form of a thin film sheet may be additionally formed on the porous first photocatalyst layer to cover the first photocatalyst layer. As described above, the second photocatalyst layer may be carbon nitride (C ₃ N ₄ ), more specifically alkali-modified carbon nitride (mC ₃ N ₄ ).

As an example, carbon nitride may be formed through thermal decomposition of a precursor compound, and alkali-modified carbon nitride is alkali-modified in a dispersion formed by adding carbon nitride formed by thermal decomposition into a liquid medium, for example, an aqueous medium. It can be modified using components. The first photocatalyst layer-nanorods/substrate structure prepared previously is brought into contact with the aqueous dispersion obtained according to the above-described method so that the second photocatalyst layer can be formed on the first photocatalyst layer.

According to an exemplary embodiment, the precursor of carbon nitride may be a compound represented by the following general formula (1).

[General formula 1]

In the above formula, X, Y and Z are the same as or different from each other, and are independently R ₁ -NR ₂ connected to a triazine ring using a nitrogen atom,

In this case, R ₁ and R ₂ are independently hydrogen, an alkyl group having 1 to 10 carbon atoms (specifically, 1 to 5 carbon atoms), a cycloalkyl group having 3 to 10 carbon atoms (specifically 3 to 5 carbon atoms), or 6 to 10 carbon atoms (specifically to C6 to C8) may be an aryl group. In a specific embodiment, X, Y and Z are all the same, and in this case, R ₁ and R ₂ may both be hydrogen. In this case, the organic compound corresponds to melamine, triazine, benzotriazole, and the like.

According to an exemplary embodiment, the thermal decomposition reaction may be carried out, for example, at a temperature in the range of about 300 to 700 °C, specifically about 400 to 600 °C, more specifically about 450 to 550 °C, so that the precursor is converted to carbon nitride. As such, carbon nitride produced by thermal decomposition is dispersed in an aqueous medium in the form of a powder, and the content of carbon nitride in the dispersion is, for example, about 0.01 to 0.5 mol/L, specifically about 0.04 to 0.3 mol/L , more specifically about 0.07 to 0.2 mol/L, but this may be understood as an example.

In addition, the alkali component added to the carbon nitride dispersion (or water product) for the purpose of reforming may be at least one selected from sodium hydroxide, potassium hydroxide, and the like, and specifically sodium hydroxide (NaOH) may be used. According to an exemplary embodiment, the concentration of the alkali component in the nitrogen carbide dispersion may range, for example, from about 0.05 to 0.3 M, specifically from about 0.05 to 0.2 M, and more specifically from about 0.05 to 0.15 M. When the concentration of the alkali component is too low, it is difficult for the carbon nitride particles to be converted into a thin film form, whereas when the concentration of the alkali component is too high, the carbon nitride exists in a fine state to block the porous structure of the underlying first photocatalyst layer. can do it Accordingly, it may be advantageous to appropriately adjust within the above-described range.

As such, the alkali-modified nitrogen carbide dispersion is contacted with the previously prepared first photocatalyst layer-nanorods/substrate structure using a known method (eg, dipping, etc.) to form the second photocatalyst layer with the first photocatalyst layer- It can be formed on the nanorod/substrate structure. At this time, the attachment temperature of the second photocatalyst layer is not particularly limited, but may be, for example, about 10 to 40° C., specifically about 15 to 30° C., more specifically about 20 to 25° C., and the contact time is, for example, For example, it may be in the range of about 10 to 60 hours, specifically about 20 to 48 hours, and more specifically about 30 to 40 hours, but this may be understood as an example.

Thereafter, the obtained structure may be selectively washed and/or dried to prepare a photocatalytic filter.

Removal of contaminants in gaseous media using photocatalytic filters (gas purification)

According to another embodiment of the present disclosure, the photocatalytic filter prepared as described above may be used to remove contaminants contained in a gas (specifically, indoor or outdoor atmosphere). At this time, the contaminant is not particularly limited as long as it is a type that can be contained in the air or indoor/outdoor atmosphere (gas phase medium).

According to an exemplary embodiment, the contaminants may be various aldehydes, volatile organic compounds (VOCs), and the like, and exemplary types of such contaminants are shown in Table 1 below.

contaminant Kinds aldehydes acetaldehyde propionaldehyde butyraldehyde isovarelaldehyde VOCs toluene styrene benzene Alcohol ketones

The contaminants exemplified above may originate from various sources, either indoors or outdoors, for example, various chemicals applied within the building. In this regard, the photocatalytic filter is effective in removing VOCs, particularly aromatic compounds, specifically benzene, toluene, and the like.

Meanwhile, the concentration of the contaminants in the gas to be treated is not particularly limited, but typically about 5 to 20000 μmol·m ⁻³ , and more typically about 100 to 12000 μmol·m ⁻³ .

In addition, during the oxidation reaction, moisture acts as a source of hydroxy radicals required for removal of contaminants, and in this case, the humidity (relative humidity (RH)) of the gas to be treated is, for example, at least about 15%, specifically about 20 to 70%. %, more specifically about 30-50%. In addition, the reaction temperature (equilibrium temperature) upon removal of contaminants in the gaseous medium by the photocatalytic oxidation reaction is, for example, in the range of about 20 to 40 °C, specifically about 25 to 35 °C, more specifically about 27 to 32 °C. may be adjusted, but this is understood as an example, and may be changed in consideration of the type of target contaminants and the like.

According to an exemplary embodiment, the decomposition of contaminants in the gaseous medium by the photocatalytic filter may be performed under ultraviolet irradiation, wherein the irradiation intensity of ultraviolet light is, for example, about 0.1 mW/cm 2 to 80 kW/cm 2, Specifically, it may be in a range of about 1 mW/cm 2 to 10 kW/cm 2 , more specifically about 10 mW/cm 2 to 1 kW/cm 2 . In this regard, as the irradiation intensity of ultraviolet light is one of the main factors affecting the photocatalytic efficiency, it may be advantageous to appropriately control it within the above-mentioned range, but as much as it can be changed according to the type, concentration, etc. of contaminants in the gas, It can be understood in an exemplary sense. In addition, the wavelength of the irradiated ultraviolet rays may be, for example, about 100 to 400 nm, specifically about 180 to 320 nm, more specifically about 230 to 280 nm.

According to an exemplary embodiment, the UV source may be an electrodeless UV lamp. The electrodeless UV lamp uses the principle that UV light is emitted by irradiating a high frequency from the outside without forming an electrode inside the vacuum tube. That is, it may be a method in which gaseous molecules such as mercury and argon charged inside the vacuum tube are excited to cause a discharge to emit ultraviolet rays. Specifically, the UV lamp may be a UV LED type.

According to an exemplary embodiment, the contact temperature of the contaminant-containing gas and the photocatalytic filter may be, for example, in the range of about 4 to 40 °C, specifically about 10 to 35 °C, more specifically about 15 to 30 °C. Since the catalytic reaction temperature may be changed depending on the type of contaminant, the above-described range may be understood for illustrative purposes.

The photocatalytic filter may have various shapes, for example, a structure having a shape such as a plate, a mesh, a tube, etc., according to a strand-type substrate or a combination structure of such substrates, and more specifically, may be applied in a mesh form.

The present invention may be more clearly understood by the following examples, which are only for illustrative purposes of the present invention and are not intended to limit the scope of the present invention.

Example

Materials used in this example are as follows.

Zinc acetate dihydrate (99%), nickel nitrate hexahydrate (99%), sodium molybdate dihydrate (99%), hexamethylenetetraamine C ₆ H ₁₂ N ₄ , 99%), urea (NH ₂ CONH ₂ , 99.5%), EDTA (C ₁₀ H ₁₆ N ₂ O ₈ , 99.9%), melamine (C ₃ H ₆ N ₆ , 99%), benzoquinone (BQ, C ₆ H ₄ O ₂ , 98%) , TBA(CH ₃ ) ₃ COH, 99.5%), DMSO ((CH ₃ ) ₂ SO, 99.5%), and sodium azide (NaN ₃ , 99%) were each purchased from Sigma Aldrich (USA).

Manufacturing method of photocatalytic filter

FIG. 2 shows the method of manufacturing the photocatalytic filter according to the present embodiment step by step.

- Synthesis of ZnO@SSM (Step I)

A 6 × 8 cm SSM (stainless steel mesh) was washed over 30 minutes under ultrasonic irradiation in an ethanol/water (1:1) solution. A solution of 15 mmol/L concentration was prepared by dissolving zinc acetate in deionized water. The SSM substrate was dipped in zinc acetate solution and covered with aluminum foil. The solution was heated in an oven at 60° C., and after 6 hours, a ZnO seed layer was formed on the SSM through ultrasonic cleaning, drying in an oven and calcination at 400° C. for 4 hours. A precursor solution of ZnO nanorods was prepared by dissolving zinc acetate (25 mmol·L ^-1 ), HMTA (20 mmol·L ^-1 ), and urea (30 mmol·L ^{-1 ) in 120 mL deionized water.} The precursor solution was transferred to a Teflon-lined autoclave along with the SSM substrate on which the ZnO seed layer was formed. The autoclave was heated for 6 hours in a furnace maintained at 120° C. so that the ZnO nanorods were uniformly grown. ZnO@SSM was washed with deionized water and ethanol (twice each) and dried at 60° C. overnight.

_{- Synthesis of NiMoO 4} Layers in ZnO@SSM (Step II)

Nickel nitrate (10 mmol·L ^-1 ), sodium molybdate (10 mmol·L ^-1 ), and urea (40 mmol·L ^-1 ) were dissolved in 500 mL deionized water to prepare a precursor solution for _{NiMoO 4 synthesis} . ZnO@SSM was suspended vertically in a beaker containing the solution, covered with aluminum foil, and heated at 80° C. for 8 hours. After 8 hours, the obtained ZnO/NiMoO ₄ @SSM (ZN@SSM) was thoroughly washed with deionized water and sonicated for 10 minutes to remove _{NiMoO 4 loosely attached to the surface.} The NiMoO ₄ deposition process was repeated to prepare ZN@SSM substrates with double and triple layers.

- _{Synthesis of mC 3} N ₄ and ZnO/NiMoO ₄ /C ₃ N ₄ @SSM (Step III)

_{C 3} N ₄ was prepared by thermally decomposing melamine at 500° C. for 4 hours in an alumina crucible equipped with a cover. _{C 3} N ₄ obtained after heating was ground in an agate mortar. While performing ultrasonic irradiation for 2 hours, C ₃ N ₄ was dispersed in 100 mL of water _{to prepare a C 3} N ₄ suspension (0.1 mol·L ^-1 ), and sodium hydroxide was dissolved therein and transferred to a Teflon-lined autoclave. Heated at 180° C. for 12 hours. _{mC 3} N ₄ was separated by centrifugation, washed with water and ethanol, covered with aluminum foil, and maintained at room temperature for 36 hours. ZNC@SSM was washed with water and ethanol and dried in an oven.

characterization

The crystal structure of the catalyst was analyzed by XRD (Rigaku D/MAXRINT 000, Japan). In this case, Cu Kα irradiation of 45 kV and 100 mA was used as an X-ray source. SEM (Nova NanoSEM 450, FEI-Thermo Fisher Scientific, USA) and TEM (JEM-2010, Jeol, Japan) were used under the condition of an accelerating voltage of 200 kV. The elemental oxidation state was measured using XPS (K-alpha, Thermo Electron, USA). UV-vis diffuse reflectance spectroscopy (Lambda 750S, PerkinElmer, USA) was used to measure the light collection potential of the catalyst.

performance evaluation

Adsorption experiments were performed in a closed glass chamber (1.9 L, 30 cm × 45 cm) under dark conditions. A toluene mixture ^{of 4000 μmol·m −3} in pure air in a 5L aluminum bag was prepared using toluene standard gas (40000 μmol·m ^{−3 in} _{pure N 2 ).} The glass chamber was flushed with pure air for 10 minutes to remove any contaminants adhering to the glass walls. ZNC@SSM (10×15 cm) was placed in the reactor and toluene (4000 μmol·m ⁻³ ) was added. After a fixed time interval, a 100 μL test sample was withdrawn from the sample port using a gas-tight syringe and analyzed by a GC equipped with an MS detector. A desorption experiment was performed by placing ZNC@SSM to which toluene was adsorbed in a glass chamber. Increasing the toluene concentration inside the glass chamber by analyzing test samples on an Agilent 7890A gas chromatography (GC) using a 5975C Series Mass Spectrometer (MS) equipped with an Agilent DB-5ms column (30 m × 250 μm × 0.25 μm) was monitored. Helium at a flow rate of 1.0 mL·min ^{−1 was used as the carrier gas.} The injector and oven temperatures were maintained at 300°C and 140°C, respectively.

The photocatalytic decomposition reaction was performed in a (1.9 L, 30 cm × 45 cm) glass reactor equipped with a UV lamp (8 W, Philips, inside quartz sleeve) in the center of the reactor. A catalyst filter of 8 annular pieces (diameter: 9 cm) was used for each photocatalytic reaction experiment. A Teflon-coated annular stainless steel stand was used to support the air filter inside the reactor. Before starting the experiment, the glass reactor was ^{flushed with 4000 μmol·m −3} toluene (air mixture) 20L to achieve adsorption-desorption equilibrium. After flushing, the reactor was sealed and the lamp turned on. Test samples were collected from the sample port and analyzed on GC/MS.

Results and discussion

Referring to FIG. 2 , in step I, a ZnO seed layer was attached to the cleaned SSM substrate by ultrasonic irradiation, and ZnO nanorods forming the primary building block of air pockets were grown on the SSM by hydrothermal synthesis. In this case, ZnO-nanorods@SSM (Z@SSM) are radially arranged, and _{a porous coating layer of NiMoO 4} is formed on the ZnO nanorods by using a wet chemical process (ZN@SSM). The method performed at such a low temperature causes only minimal damage to the nanorods. For step II, it was repeated to achieve _{a NiMoO 4} thickness that improved gas exchange across the catalyst surface.

_{C 3} N ₄ was synthesized through thermal decomposition of the melamine precursor, and converted into a fine thin film sheet through high-temperature alkali treatment of _{C 3} N ₄ , and was attached to ZN@SSM from _{mC 3} N _{4 suspension.} The final assembly and structure of the ZNC@SSM is as shown in Fig. 2 (Step III).

- SEM, TEM and EDS mapping

Step-by-step growth and assembly of ZN@SSM nanostructures were confirmed using SEM, TEM and EDS mapping. FIG. 3A shows an SSM (square hole size: 120 μm) of a 1×1 plain weave structure. The small pores in the SSM are large enough to maintain maximal interaction between the catalyst and gas molecules, and also to allow for smooth airflow during the calcination process. The diameter of the single SSM strand was 50 ± 1 μm (Fig. 3b). ZnO nanorods were uniformly grown along the SSM surface (Fig. 3d). As it was observed that the ZnO seed layer had a significant effect on the growth of ZnO nanorods, ZnO nanorods grew vertically at uniform intervals on the SSM substrate with the seed layer formed (Fig. 3d and 3e). In the absence of the seed layer, the ZnO nanorods insufficiently covered the SSM (Fig. 4a and 4b). The ZnO nanorods exhibited a conical shape with an average length of 500 ± 50 nm. The bottom and top diameters were 100±10 nm and 50±10 nm, respectively ( FIG. 3f ). The ZN@SSM catalyst at the end of stage II is shown in Figure 3g.

NiMoO ₄ was grown in the shape of a petal on the upper layer of the ZnO nanorods in the form of a hexagonal thin plate (FIG. 3h). The TEM result shows that _{the average size of NiMoO 4} petals is about 300 ± 50 nm (Fig. 4c). The NiMoO ₄ layer thickness affects the adsorption capacity of the ZNC@SSM catalyst, and the optimum thickness was achieved by repeating step II twice, resulting _{in the formation of a 550 ± 50 nm thick NiMoO 4} layer (Fig. 4e). Figure 3i shows the plane of ZNC@SSM after step III. By alkali treatment of C ₃ N ₄ , the bulk structure was changed to a uniform thin film sheet. mC ₃ N ₄ uniformly surrounded the NiMoO ₄ petals (Fig. 3i), while untreated C ₃ N ₄ was attached in a random manner (Fig. 4f). The thin film-like structure of the C ₃ N ₄ sheet was improved with increasing NaOH concentration up to 0.1 M. At 0.2 M NaOH, a very sensitive sheet structure was formed, but the porous NiMoO ₄ layer was occluded (Fig. 4g). Maximum toluene absorption was achieved by performing alkali treatment on _{C 3} N ₄ in the bulk state using 0.1 M NaOH. EDS mapping results show compositional and spatial distribution within ZNC@SSM ( FIGS. 3J to 3O ). All essential elements were present in ZNC@SSM. _{mC 3} N ₄ sheets on the NiMoO ₄ layer were also identified ( FIGS. 3n and 3o ).

- XRD analysis

The crystal structure and catalytic growth of the SSM phase were characterized using XRD (Fig. 5). According to the diffraction pattern of Z@SSM, three main peaks were observed at 31.7°, 34.9°, and 36.4°, which are (100), (0002), and (101) Miller-Bravais planes (JCPDS no. 36- 1451). The irregular orientation of the ZnO nanorods reduces the peak intensity at 34.9°. In Fig. 5a, the strong diffraction signal at 34.9° indicates that the growth of ZnO nanorods starts from the nucleus in the seed layer and propagates vertically in the [002] direction (Fig. 5b). The random orientation of the nanorods occurs in the absence of a seed layer (Fig. 5c), and the high peak intensity at 34.9°C indicates that the nanorods with hexagonal tips are formed due to propagation of the (0002) plane (Fig. 5d).

In the SEM analysis, a sharp-shaped nanorod was also observed, which is attributed to the (003) plane (JCPDS no. 33-0948). _{The diffraction pattern of NiMoO 4} observed in N@SSM was different from that in ZNC@SSM. The two main peaks at 50.7° and 74.3° in N@SSM were absent in ZNC@SSM. This discrepancy suggests that _{the growth of NiMoO 4} occurs differently on SSM (N@SSM) and ZnO nanorods (ZNC@SSM). _{Direct growth of NiMoO 4} on SSM formed flower-like plates with fibrous diffused edges. The extraneous peaks at 50.7° and 74.3° originate from needle-like fibers, which were previously observed in _{NiMoO 4 nanorods. A sharp, well-defined edge in NiMoO 4} grown on ZnO in ZNC@SSM replaced the fibrous edge (Fig. 5g). The peaks at 50.7° and 74.3° disappeared in ZNC@SSM because there was no nanoneedle-like structure at the edge _{of the NiMoO 4 plate.} mC ₃ N ₄ showed a broad peak at 27.6°, which supports the formation of a porous amorphous structure. mC ₃ N ₄ The peak signal could not be specified in the ZNC@SSM spectrum due to the amorphous and thin sheet-like structure. The main peaks of ZnO and NiMoO ₄ appeared in the diffraction pattern of ZNC@SSM (Fig. 5a). Overall, the XRD results provide morphological results for better recognition with respect to the structural evolution of catalyst components.

- XPS analysis

The growth of the ZnO seed layer on the SSM was confirmed by XPS analysis (Fig. 6a). Zn 2p spectra of all catalysts showed binding energy peaks at 1022.5 eV and 1045 eV. This peak position ^{corresponds to the Zn 2+} oxidation state, which is consistent with the metal oxide form (ZnO). The two peaks at 856 eV and 874 eV along with the respective satellite peaks in FIG. 6b are associated with ^{Ni 2+ species.} Molybdenum was present in the Mo ⁶⁺ state (FIG. 6c). The peaks related to the metallic forms of Ni and Mo, respectively, were not observed in the Ni 2p and Mo 3d spectra. The C 1s spectrum in FIG. 6d showed two distinct binding energy peaks. The broad signal around 285 eV is from CC and CO binding. The peak at 288 eV may be due ^{to sp 2} hybridized carbon atoms bonded to nitrogen atoms in C=N, C≡N, and NC=N. The peak intensity at 288 eV increased after hydrothermal alkali treatment, indicating that the graphite domain in the _{C 3} N _{4 matrix was improved.} The improved graphite is beneficial for the electronic conductivity of the catalyst. 6e, the peak at 530 eV is a characteristic value of oxygen bound to a metal atom (ZnO and NiMoO ₆ ). An additional peak between 531.5 eV and 532.5 eV was observed after _{C 3} N _{4 incorporation into the catalyst structure.} These peaks are from C=O/CO groups on the _{C 3} N _{4 surface.} The light absorption capacity of the catalyst was observed using DRS (diffuse reflectance spectroscopy). ZnO, NiMoO ₄ , and C ₃ N ₄ exhibited excellent light absorption in the UV region ( FIG. 6f ). Visible light absorption was indicated by NiMoO ₄ , and C ₃ N ₄ . The light absorption range of ZNC@SSM was similar to its constituents, although slightly improved. The band gap energy was determined using the Tauq equation and the Kubelka-Munk function. Edge positions of conduction and valence bands were calculated from ultraviolet photoelectron spectroscopy (UPS). The band gap energy and band edge position are shown in FIG. 6H and Table 2 below.

No. catalyst band gap
(eV) conduction band
(eV) home appliance stand
(eV) One ZnO 3.1 -0.17 2.93 2 NiMoO ₄ 2.54 0.16 2.70 3 C ₃ N ₄ 2.69 -1.14 1.54

- Performance evaluation

The gentle adsorption of VOCs before the photoreaction is essential to maintain a desirable decomposition reaction rate. Experiments on the kinetics of gaseous toluene (4000 μmol·m ⁻³ of toluene in pure air) adsorption onto the catalyst were carried out in a closed glass chamber. Toluene adsorption on the glass wall was negligible in the blank test. According to FIG. 7a , the toluene adsorption on inorganic surfaces of SSM and N@SSM ^{was less than 1 μmol·m −2} , which was consistent with low affinity for organic molecular species. On the other hand, ZnO, an inorganic component, exhibited twice the adsorption capacity compared to SSM and N@SSM. The good toluene adsorption to ZnO is related to chemisorbed oxygen species, which attract electrons from ZnO due to their high electron affinity.

The decrease in electron density creates a depleted layer near the ZnO surface. Reducing gases (eg toluene with a π-electron system, benzene and their derivatives) are susceptible to oxidation due to the depleted layer in ZnO. The oxidation reaction proceeds in a two-step indirect manner: (i) gas molecules react with adsorbed oxygen species (O ₂ ⁻ , O ⁻ , and O ^{2 −} ), and (ii) oxygen transfers electrons from toluene molecules. and release the previously captured electrons into the ZnO. In order to confirm this mechanism, an adsorption experiment was performed using ^{toluene (4000 μmol·m −3 ) diluted in argon.} Prior to the adsorption experiment, the glass chamber equipped with the Z@SSM catalyst was flushed with nitrogen for 15 minutes to remove most of the oxygen adsorbed on the ZnO surface. Toluene adsorption in the absence of oxygen ^{was reduced to 0.8 μmol·m −2} , which supports the proposed toluene adsorption mechanism.

The adsorption capacity of N@SSM _{was enhanced after attachment of mC 3} N ₄ (Fig. 7a), and the increase of 77% was judged to be due to the triazine ring _{in C 3} N _{4 , which is similar to toluene and better than NiMoO 4} adsorption site. provides Air pockets were formed after coating Z@SSM with _{NiMoO 4 .} The presence of air pockets is confirmed by the substantial increase in toluene adsorption by ZN@SSM and ZNC@SSM. The alveolar structures of ZN@SSM and ZNC@SSM ^{adsorbed 4.4 μmol·m -2} and 6.1 μmol·m ^-2 of toluene, respectively. The two-step mechanism of the improved toluene adsorption to the catalyst is shown in Figure 7b.

Toluene is initially adsorbed inside the air pocket due to its high ZnO affinity, and then induces a concentration gradient to diffuse from the high concentration region (outside the air pocket) to the low concentration region (inside the air pocket). The instantaneous diffusion continues until the maximum space inside the air pocket is filled with toluene molecules.

Referring to FIG. 7A , a point of refraction was observed for adsorption rates with the ZN@SSM and ZNC@SSM catalysts, indicating the point of maximum space filling in the air pocket. After this point, the adsorption mechanism switches to the second phase, and the molecules are adsorbed on the outer surface of the catalyst (Fig. 7b). The second slope in the rate of adsorption to the catalyst is due to continued adsorption on the outer surface. A similar trend is observed for toluene desorption (Fig. 7c). ZN@SSM and ZNC@SSM showed two-step desorption kinetics. The small arc in the initial stage and the large arc in the subsequent stage correspond to toluene desorption from the outer and inner surfaces of the air pockets, respectively (Fig. 7d). Two-step adsorption was only applicable for ZN@SSM and ZNC@SSM, whereas the other catalysts showed a single slope and curve. A gentle desorption rate allows the toluene to be photolysed without poisoning the catalyst surface. Overall, the adsorption tendency supports the presence of air pockets in the catalyst, meaning that toluene molecules can be adsorbed from air without the use of any adsorbent.

As shown in FIG. 8, a photocatalytic conversion reaction of toluene was performed in a sealed Pyrex glass reactor. In the figure, the reaction apparatus consists of a glass reactor (1), an aluminum bag (2), a thermometer (3), a UV lamp (4), a photocatalytic filter (5), a sampling port (6) and a Teflon-coated stand (7). ) is configured to include

A blank test was performed in the presence or absence of light to evaluate the self-decomposition of toluene molecules. The little effect on toluene concentration in the blank test supports the integrity of the glass reactor for gas phase experiments. As shown in FIG. 9A , SSM exhibited inactivity until the catalyst was mounted.

For Z@SSM and N@SSM, 15% and 8% of toluene was decomposed after 120 minutes, respectively. The fact that a higher amount of toluene is decomposed using Z@SSM may be due to the selectivity and higher absorption capacity compared to N@SSM. The toluene decomposition rate was slightly improved in NC@SSM. This is due to the proper band edge alignment between _{NiMoO 4} and mC ₃ N _{4 ( FIG. 6h ).} ZN@SSM and ZNC@SSM significantly increased the decomposition rate of toluene under the same conditions. This performance improvement results from the mass transfer of the novel catalyst. In the case of the conventional photocatalytic oxidation system, the adsorption was limited because it entailed blocking of the catalyst surface. In this embodiment, the poisoning of the catalyst can be suppressed by spatial separation of the adsorption site (inside the air pocket) and the catalytically active site (NiMoO ₄ /mC ₃ N _{4 layer).} The advantage of the alveolar-like structure is that the influx of VOCs (40 μmol m ^-3 , 2000 μmol m ^-3 , 4000 μmol m ^-3 , 8000 μmol m ^-3 , and 12000 μmol m ^-3 ) It can be further analyzed by analyzing the sensitivity of the catalyst. On the other hand, Z@SSM, N@SSM, and NC@SSM showed little adsorption/catalytic activity at a toluene concentration ^{of 40 μmol·m −3 ( FIG. 10 ).}

This deactivation was due to the catalyst not properly interacting with the toluene molecules. The catalytic decomposition reaction by Z@SSM, N@SSM, and NC@SSM was ^{improved by increasing adsorption at toluene concentrations of 2000 μmol·m −3} and 4000 μmol·m ⁻³ ( FIGS. 10b and 10c ). After 4000 μmol·m ⁻³ , the decomposition performance of the catalyst with a non-alveolar structure was stagnant ( FIGS. 10d and 10e ). The adsorption predominance at 8000 μmol·m ⁻³ and 12000 μmol·m ⁻³ is evident from the decrease in the ratio (C/A ratio) of catalytic removal to adsorption removal of toluene (see Table 3 below).

catalyst Toluene inlet concentration (mol ³ ) 40 2000 4000 8000 12000 SSM 0.0 1.6 2.5 1.5 1.1 Z@SSM 2.4 3.0 5.4 4.4 3.6 N@SSM 0.0 4.0 6.0 4.3 3.4 NC@SSM 4.0 6.5 7.8 6.4 5.0 ZN@SSM 9.0 9.7 10.7 10.3 9.9 ZNC@SSM 9.2 9.7 10.6 10.5 9.8

Unlike catalysts having a non-alveolar structure, ZN@SSM and ZNC@SSM showed stable decomposition performance irrespective of the toluene input concentration ( FIGS. 10a to 10e ). The C/A ratio of the catalyst having an alveolar structure suggests that the decomposition reaction by the catalyst is not affected by the toluene concentration change. At high concentrations, the mass load of contaminants on the catalytically active site is reduced by preferentially storing molecules inside air pockets, while at low concentrations, the alveolar-structured catalyst physically traps toluene molecules and functions as a reservoir for continuous supply to the reaction site. make this happen This novel concept of molecular trapping method can provide superior decomposition performance compared to conventional catalysts. The results of the toluene adsorption and photolysis reaction are summarized in Table 4 below.

catalyst Toluene adsorption
(μmol·m ^-2 ) toluene decomposition rate
(%) decomposition rate
(μmol h ^-1 m ^-2 ) SSM 0.6 2.2 0.8 Z@SSM 1.9 15 5.2 N@SSM 0.9 8 2.7 NC@SSM 1.6 19 6.5 ZN@SSM 4.4 68 23.2 ZNC@SSM 6.1 95 32.7

The effect of C ₃ N ₄ modification on toluene decomposition was analyzed (FIG. 9b). Intrinsic C ₃ N ₄ aggregated and formed fragmented contacts with petal-shaped NiMoO ₄ ( FIG. 9d ). As a result, the toluene decomposition rate was 81% due to low adsorption and inefficient charge carrier transport. The granular structure of C ₃ N ₄ was converted into a thin sheet after high-temperature alkali treatment. _{mC 3} N ₄ treated with 0.1 M NaOH surrounded the petal-shaped NiMoO ₄ ( FIG. 9e ), and formed a uniform porous structure showing the highest toluene decomposition rate (95%). When treated with 0.2 M NaOH, mC ₃ N ₄ was excessively purified and _{blocked the NiMoO 4} layer ( FIG. 9f ), and the toluene decomposition rate was reduced to 74%.

The effect _{of the thickness of the NiMoO 4} layer on the toluene decomposition rate was analyzed (FIG. 11). NiMoO ₄ layers were prepared using 1, 2 and 3 adhesion cycles, forming layer thicknesses of 0.2-0.3 μm, 0.5-0.6 μm, and 0.9-1.0 μm, respectively ( FIGS. 11A-11C ). The thickness of the NiMoO ₄ layer had a significant effect on the toluene decomposition rate, which could be explained by molecular diffusion across the _{NiMoO 4 layer.} For a single attachment cycle, the NiMoO ₄ layer was not sufficient to trap the toluene molecules inside the air pockets (Fig. 11d). A toluene decomposition rate of 81% was obtained under high diffusion across the NiMoO _{4 layer.} The optimal thickness was achieved in two attachment cycles because it formed a uniform porous structure that balances the inflow and outflow of molecules from the air pockets. The NiMoO ₄ layer is in a dense or dense state after 3 adhesion cycles. As shown in Fig. 10f, molecular diffusion is _{hindered by the complex NiMoO 4} structure, which reduces the decomposition performance by 71%.

12A shows the effect of temperature on toluene decomposition. In the catalytic reaction experiments, the temperature was controlled by cooling the lamp jacket by a continuous air flow, and the temperature was limited to 26 ± 0.5 °C.

To analyze the temperature effect, the air flow was stopped and the reactor was allowed to attain the true temperature under irradiation. As shown in Fig. 12a, the temperature increased rapidly after the initial 60 min, and equilibrium was achieved at 31 0.5 °C.

The temperature rise inside the reactor promotes the kinetic energy of molecules, which affects the interaction between the adsorption site and the catalytically active site. These adverse effects are reflected in the reaction rate and the toluene decomposition reaction by ZNC@SSM. In batch reactors, the performance decrease with increasing temperature can be reduced in continuous flow reactors because of the cooling effect of the air flow through the reactor. In this regard, it is believed that the ZNC@SSM can operate without temperature control in a continuous flow reactor, as it requires a gentle cooling airflow.

In a photocatalytic oxidation reaction system, relative humidity (RH) can change the decomposition performance by influencing the ROS generation and decomposition pathways of the target VOC. To evaluate this effect, toluene decomposition experiments at five RH levels were performed (12b). At low RH (20% and 30%), the toluene decomposition rates were 73% and 84%, respectively. The poor performance at low RH is related to the slower generation of hydroxyl radicals as the amount of moisture absorbed on the catalyst layer is reduced. At higher RH levels, ie, 50% and 60%, the toluene decomposition rate decreased due to competitive adsorption between moisture and toluene molecules. A balance between adsorption and ROS generation was achieved at 40% RH, which was the best result of the selected RH levels.

ROS generation and its relative participation in catalysis were analyzed by scavenging experiments. Using DMSO, benzoquinone (BQ), ethylenediamine tetraacetic acid (EDTA), TBA and sodium azide (NaN ₃ ), electrons, superoxide radicals (·O ^{2 −} ) holes, hydroxy radicals (·OH) and Each of singlet oxygen ( ¹ O ₂ ) was removed. 12C shows the normalized effect of the scavenger on the decomposition performance of the catalyst in this example. DMSO, BQ, EDTA, and TBA inhibited toluene decomposition by Z@SSM, indicating that electrons, hydroxy radicals (.OH), holes and .O ^{2 -} exist on the catalyst surface, respectively.

In N@SSM and ZN@SSM, hydroxy radicals in the valence band (VB) were the main reactive active species, whereas ·O ^{2 −} radicals had little effect on the decomposition activity. The unbalanced role of ROS associated with VB/CB in N@SSM and ZN@SSM is due to the lower reduction potential of CB _{in NiMoO 4 .} In the ZN@SSM, the ZnO nanorods were coated with a layer of _{NiMoO 4} , which suppressed the generation ^{of ·O 2 − radicals in the CB of ZnO.} In ZNC@SSM, the -OH radical and the -O ₂ ^- radical were involved in toluene decomposition. ·O ^{2 - The} species contributed more in ZNC@SSM than in ZN@SSM. ·O ₂ ⁻ radicals are _{cheaply generated in the CB of mC 3} N ₄ , whereas ZnO was relatively passive in the catalytic reaction ( FIG. 12d ). For the individual catalysts, the inhibition of decomposition by the electron scavenger was very similar to the inhibition of the decomposition by the ^{·O 2 - scavenger, suggesting that the ·O 2 -} radical was mainly generated by photoexcited electrons.

In FIG. 12C , the inhibition of decomposition by the hole scavenger did not coincide with the inhibition of decomposition by the OH scavenger. This indicates that some reactive species other than ·OH were also generated at VB of the catalyst. To analyze this discrepancy, a ¹ O ₂ scavenger was used and a reduction in toluene decomposition was observed. In this regard, some ·O ^{2 −} radicals were ^{oxidized to 1} O ₂ species, which explains the difference between inhibition of decomposition by hole and ·OH scavengers. The reusability potential of the ZNC@SSM air filter was evaluated through repeated toluene decomposition experiments. After each decomposition experiment, ZNC@SSM was immersed in deionized water (40 °C, 30 min), dried, and reused in the next experiment. The ZNC@SSM filter maintained excellent catalytic performance during the reuse test process, and maintained a toluene decomposition rate of more than 90% even after 10 cycles (FIG. 13).

In FIG. 14 , the SEM results supported the integrity of the catalyst film after washing and cycle decomposition tests were performed. Although there was a slight peak change, the XRD and XPS spectra of ZNC@SSM before and after the test were almost identical ( FIGS. 14b to 14f ). Overall, the photocatalytic performance and characterization results suggest that the ZNC@SSM filter is durable against washing and has good reuse potential for VOC degradation.

Toluene decomposition pathways under low relative humidity (20%) and high relative humidity (40%) conditions were analyzed. At 20% RH, toluene decomposition ^{proceeded by attack of the ·O 2 -} radical, indicating that it is the main decomposition pathway ( FIG. 15 ). First, after cleavage of the double bond in the toluene ring, hydrogen was added to form 1-cyclohexene-1-carboxyaldehyde. In the second step, benzoic acid was identified, which was converted to a mixture of butadiene and acetone in the third step. After 20 minutes, a short chain carboxylic acid was formed, which was converted to carbon dioxide in the final step. At 40% RH, moisture adsorbed to the catalyst surface generated .OH radicals, which formed benzoic acid directly from toluene. In the second step, a mixture of acetic acid and formic acid was detected inside the reaction, which was converted to carbon dioxide in the third step. The oxidative route of toluene decomposition was much faster than the alternative reduction route. The intermediates in the second and fourth steps of the reduction route were not formed in the course of the oxidative decomposition reaction. It is believed that a shorter cracking path leads to better catalytic performance at higher RH conditions.

The photon flux required for the decomposition of toluene molecules was determined by calculating the apparent quantum yield (AQY) of the photocatalytic process, and is shown in Table 5 below.

photocatalyst
VOCs
light source
energy consumption
(Wh) filter size
(m ² ) Conversion VOC
(umole) AQY
FOM
TiO ₂ benzene UV 1200 0.003 2.4 8.51×10 ^-08 1.6 N ₂ doped TiO ₂ benzene UV 1200 0.003 23.5 1.18×10 ^-06 15.7 Bi ₂ O ₂ CO ₃ toluene Vis 600 0.066 12.3 1.25×10 ^-06 0.4 CuS/Bi ₂ O ₂ CO ₃ toluene Vis 600 0.066 18.6 1.86×10 ^-06 0.6 CdS/Bi ₂ O ₂ CO ₃ toluene Vis 600 0.066 22 2.18×10 ^-06 0.7 CuS/CdSBi ₂ O ₂ CO ₃ toluene Vis 600 0.066 39.8 4.60×10 ^-06 1.2 Fe/TiO ₂ toluene UV 20 0.007 0.8 9.98×10 ^-06 19.4 PVP Modified TiO ₂ acetone UV 208 0.007 8.3 4.42×10 ^-06 2.4 PVP Modified TiO ₂ benzene UV 916 0.007 1.8 2.96×10 ^-07 0.12 TiO ₂ benzene UV 500 0.011 5.2 2.20×10 ^-06 5.9 ZNC@SSM toluene UV 12 0.113 22 4.14×10 ^-05 30.8

According to the table above, the AQY of ZNC@SSM was 10 times better than that of the previously reported PCO system. The contrast of AQY is useful for distinguishing materials based on catalytic performance. However, AQY alone cannot be considered as an absolute criterion for the selection of a PCO system. A figure of merit (FOM) reflects an important operating parameter, and can be expressed by Equation 1 below.

[Equation 1]

According to the above table, the catalysts reported previously have significant limitations at low concentrations. On the other hand, ZNC@SSM showed high catalytic activity even at low concentration due to balanced performance characteristics.

All simple modifications or changes of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will be made clear by the appended claims.

Claims (19)

substrates in the form of strands;
a nanorod array radially formed on the surface of the strand-shaped substrate in the longitudinal direction; and
a porous first photocatalyst layer formed on the nanorod array;
includes,
Here, as the porous first photocatalytic layer is coated on the nanorod array, the photocatalytic filter forms a physical trapping structure in the form of an air pocket. The photocatalytic filter according to claim 1, wherein the porous first photocatalyst layer consists of one or two or more layers, and the total thickness is in the range of 200 to 800 nm. The photocatalytic filter according to claim 2, wherein when the porous first photocatalyst layer consists of two or more layers, the thickness of each first photocatalyst layer is set in the range of 100 to 300 nm. According to claim 1, wherein the material of the nanorod array, zinc oxide (ZnO), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), cobalt oxide (Co ₃ O ₄ ), tin oxide (SnO ₂ ), Nickel oxide (NiO) and manganese oxide (MnO ₂ ) Photocatalytic filter, characterized in that at least one selected from the group consisting of. The photocatalytic filter of claim 1, wherein the porous first photocatalyst layer is formed as a thin film plate having a flower petal shape. The photocatalytic filter according to claim 5, wherein the thin-film plate is a hexagonal thin-film plate. The method of claim 1 , wherein the porous first photocatalyst layer comprises metal molybdate (MMoO ₄ ) (M is selected from Group VIII and Group IB metals), NiCo ₂ O ₄ , NiCo ₂ S ₄ , CdS, Bi ₂ WO ₆ , SnO ₂ , ZrO ₂ , Fe ₂ O ₃ , and WSe ₂ Photocatalytic filter, characterized in that at least one selected from the group consisting of. According to claim 1, wherein the photocatalytic filter further comprises a second photocatalyst layer in the form of a thin film sheet coated on the porous first photocatalyst layer,
At this time, the second photocatalyst layer is carbon nitride (C ₃ N ₄ ), silicon carbide (SiC), gallium nitride (GaN), graphene oxide, carbon quantum dots, silver chloride (AgCl), silver bromide (AgBr), zinc selenide (ZnSe), cerium oxide (CeO ₂ ), and cadmium sulfide (CdS) photocatalytic filter comprising at least one selected from the group consisting of. The photocatalytic filter of claim 8 , wherein the second photocatalytic layer comprises alkali-modified carbon nitride (C ₃ N ₄ ). The method according to claim 1, wherein the size (diameter) and length of the individual nanorods constituting the nanorod array are set within the ranges of 50 to 150 nm and 400 to 600 nm, respectively, and the aspect ratio of the individual nanorods is 4 A photocatalytic filter, characterized in that in the range of 12 to 12. The method of claim 1, wherein the strand-shaped substrate is at least one material selected from the group consisting of stainless steel (SUS), nickel foam, copper foam, glass, and aluminum foil, and
The substrate in the form of a strand is selected from the group consisting of (i) a substrate in the form of a single strand, or (ii) a mesh structure, a porous metal/non-metal foam, and a woven/non-woven fabric. A photocatalytic filter, characterized in that in the form of a structure. a) providing a substrate in the form of strands;
b) contacting the precursor solution for forming nanorods with the substrate in the form of a strand to radially form a nanorod array along the length direction thereof; and
c) contacting the photocatalyst precursor solution with the nanorod array to form a porous first photocatalyst layer on the nanorod array;
includes,
Here, a method of manufacturing a photocatalytic filter in which a porous first photocatalyst layer is coated on the nanorod array to form a physical trapping structure in the form of an air pocket. The method of claim 12, wherein step b) comprises:
b1) forming a seed layer of the nanorods on the strand-shaped substrate; and
b2) performing a hydrothermal synthesis reaction by contacting the precursor solution for forming the nanorods to the substrate on which the seed layer is formed;
A method of manufacturing a photocatalytic filter comprising a. [13] The method of claim 12, wherein d) a second photocatalyst layer in the form of a thin film sheet is additionally formed on the porous first photocatalyst layer to form a uniform porous structure;
At this time, the second photocatalyst layer is carbon nitride (C ₃ N ₄ ), silicon carbide (SiC), gallium nitride (GaN), graphene oxide, carbon quantum dots (carbon quantum dots), silver chloride (AgCl), Silver bromide (AgBr), zinc selenide (ZnSe), cerium oxide (CeO ₂ ), and cadmium sulfide (CdS) A method of manufacturing a photocatalytic filter comprising at least one selected from the group consisting of. The method according to claim 12, wherein the precursor for forming nanorods in step b) is nitrate, sulfate, acetate, formate, halide, hydroxide, a combination thereof, or a hydrate thereof as a precursor of a transition metal oxide, and
The method of manufacturing a photocatalytic filter, characterized in that the precursor solution for forming the nanorods further contains hexamethylenetetraamine, ethylenediamine, ammonia, polyethyleneimine, urea, or a combination thereof. The photocatalyst according to claim 12, wherein in step b), the nanorod array grows anisotropically with respect to the surface of the strand-shaped substrate, wherein the growth direction is in the range of 60 to 120° with respect to the surface of the substrate. A method of manufacturing a filter. A method for removing contaminants in a gaseous medium comprising:
providing a photocatalytic filter; and
oxidizing and removing the contaminants in the gaseous medium by contacting the gas containing the contaminants with the photocatalytic filter under ultraviolet irradiation,
Here, the photocatalytic filter is
substrates in the form of strands;
a nanorod array radially formed on the surface of the strand-shaped substrate in the longitudinal direction; and
a porous first photocatalyst layer formed on the nanorod array;
includes,
Here, as the porous first photocatalyst layer is coated on the nanorod array, a method of forming a physical trapping structure in the form of an air pocket. 18. The method of claim 17, wherein the contaminant is at least one selected from the group consisting of aldehydes and volatile organic compounds (VOCs), and
Method, characterized in that the concentration of contaminants in the gaseous medium is in the range of 5 to 20000 μmol·m ^{-3 .} 18. The method of claim 17, wherein the relative humidity of the gaseous medium is at least 15%, and
The method of claim 1 , wherein the step of removing the contaminants by oxidation is performed in the range of 20 to 40°C.

Images